On my video on Andrew Martin’s game with the King’s Indian Attack and a 1.g3 move order I mentioned that this should really only be played by very experienced players. There’s also a lot more to it than that.
The basic problem is that openings with flexible openings make great demands on someone’s positional play because they can resolve themselves into many different types of pawn structure. The least flexible of these, and therefore the easiest to understand is the King’s Indian Attack in which White plays e2-e4 and often e4-e5. The English tends to be considerably harder to play well (there are many possible ways you can arrange your pawns) and 1.g3 even more difficult.
So for a relatively inexperienced player or one whose positional play has not been highly developed it’s much better to play something much more direct in which the position of the central pawns is decided early on and the plans become relatively clear. The London System tends to be very good for this as do the Colle-Zukertort and Torre Attack, and after 1.e4 there are good choices in the f4 Sicilian and Scotch. And if you’re under 1400 you don’t really need to think about these things at all, just get your pieces out and try to assimilate an understanding of a few classic game plans!
One of the reasons more sophisticated openings tend to be popular with Grandmasters is BECAUSE they are so difficult for less experienced players to get to grips with, so they can outplay their oppoents much more easily. When beginners play such lines they are not doing themselves any favours, the structural and planning issues will be too complex until they’ve mastered simpler concepts. And they’ll never master the basics whilst wallowing in a sea of flexibility.
There’s a lot more I’d like to say on this matter, for example I seriously wonder who many chess products are aimed at when they’re way too sophisticated for the likes of me! But I’ll blog about that another day.